Banded iron formation

Banded iron formations (also known as banded ironstone formations or BIFs) are distinctive units of sedimentary rock that are almost always of Precambrian age.

A typical banded iron formation consists of repeated, thin layers (a few millimeters to a few centimeters in thickness) of silver to black iron oxides, either magnetite (Fe3O4) or hematite (Fe2O3), alternating with bands of iron-poor shales and cherts, often red in color, of similar thickness, and containing microbands (sub-millimeter) of iron oxides.[1]

Some of the oldest known rock formations (having formed ca. 3,700 million years ago), are associated with banded iron formations.[2] Banded iron formations account for more than 60% of global iron reserves, and can be found in Australia, Brazil, Canada, India, Russia, South Africa, Ukraine, and the United States.[3][4]

Origins

The formations are abundant around the time of the great oxygenation event,[5] 2,400 million years ago (mya or Ma), and become less common after 1,800 mya[6] with evidence pointing to intermittent low levels of free atmospheric oxygen.[7]750 million years ago new banded iron formations formed that may be associated with the theoretical Snowball Earth.[8]

An ashtray carved out of a soft form of banded ironstone from the Barbeton Supergroup in South Africa. The red layers were laid down when Archaean photosynthesizing cyanobacteria produced oxygen that reacted with dissolved iron compounds in the water, to form insoluble iron oxide (rust). The white layers are sediments that settled when there was no oxygen in the water.[9]

The conventional hypothesis is that the banded iron layers were formed in sea water as the result of oxygen released by photosyntheticcyanobacteria. The oxygen then combined with dissolved iron in Earth's oceans to form insoluble iron oxides, which precipitated out, forming a thin layer on the ocean floor, which may have been anoxic mud (forming shale and chert). Each band is similar to a varve, to the extent that the banding is assumed to result from cyclic variations in available oxygen. It is unclear whether these banded ironstone formations were seasonal, followed some feedbackoscillation in the ocean's complex system or followed some other cycle.[10][11] It is assumed that initially the Earth started with vast amounts of iron and nickel dissolved in the world's acidic seas. As photosynthetic organisms generated oxygen, the available iron in the Earth's oceans precipitated out as iron oxides. At a suspected tipping point where the oceans became permanently oxygenated, small variations in oxygen production produced periods of free oxygen in the surface waters, alternating with periods of iron oxide deposition.

Formation Process

Algoma-type

Algoma-type are generally smaller in size and formed primarily in the Archean. Algoma-type BIFs are generally found in volcanic rocks in greenstone belts. The formation process involves the chemical precipitation of iron in anoxic environments. When oxidized the iron would precipitate and sink to the bottom of the seafloor. As the oxygen levels continuously shift, we can see magnetite beds interlayered with amorphous/microcrystalline quartz (i.e. jasper).[3][4][12]

Superior-type

Superior type are the second and larger form of BIFs. They primarily formed during the Paleoproterozoic era, occurring on continental shelves and can be found around the world.[3][4][12] Superior types were formed by chemical precipitation in shallow waters, primarily due to the low atmospheric and ocean oxygen levels, resulting in high iron levels in the oceans. Under calm shallow conditions, oxygen released during photosynthesis by blue-green algae, would combine with the iron creating magnetite, which would then sink and deposit on the floor.[13]

Snowball Earth

Until 1992[14] it was assumed that the rare, later (younger) banded iron deposits represented unusual conditions where oxygen was depleted locally. Iron-rich waters would then form in isolation and subsequently come into contact with oxygenated water. The Snowball Earth hypothesis provided an alternative explanation for these younger deposits. In a Snowball Earth state the continents, and possibly seas at low latitudes, were subject to a severe ice age circa 750 to 580 million years ago (mya) that nearly or totally depleted free oxygen. Dissolved iron then accumulated in the oxygen-poor oceans (possibly from seafloor hydrothermal vents). Following the thawing of the Earth, the seas became oxygenated once more causing the precipitation of the iron.

An alternative mechanism for banded iron formations in the Snowball Earth era suggests the iron was deposited from metal-rich brines in the vicinity of hydrothermally active rift zones.[15] Alternatively, some geochemists suggest that banded iron formations could form by direct oxidation of iron by microbial anoxygenic phototrophs.[16]

Sudbury Basin impact

Banded iron formations in northern Minnesota were found directly underneath a thick layer of ejecta from the Sudbury Basin impact. At the time of formation Earth had a single supercontinent called Columbia with substantial continental shelves. An asteroid (estimated at 10 km across) slammed into waters about 1,000 m deep some 1.85 billion years ago. Computer models suggest that the tsunami would have been at least 1,000 metres high at the centre, and 100 metres high about 3,000 kilometres away. Those immense waves and large underwater landslides triggered by the impact stirred the ocean, bringing oxygenated waters from the surface down to the ocean floor.[6]

Sediments deposited on the seafloor before the impact, including banded iron formations, contained little if any oxidized iron (Fe(III)), but were high in reduced iron (Fe(II)). This Fe(III) to Fe(II) ratio suggests that most parts of the ocean were relatively devoid of oxygen. Marine sediments deposited after the impact included substantial amounts of Fe(III) but very little Fe(II). This suggests that sizeable amounts of dissolved oxygen were available to form sediments rich in Fe(III). Following the impact dissolved iron was mixed into the deepest parts of the ocean. This would have choked off most of the supply of Fe(II) to shallower waters where banded iron formations typically accumulated.

The geological record suggests that environmental changes were happening in oceans worldwide even before the Sudbury impact. The role of the Sudbury Basin impact in temporarily shutting down banded iron formation accumulation is not fully understood.

The Chichester Range is a range in the Pilbara region of Western Australia.

The range rises abruptly from the coastal plain and is composed of rolling hills, escarpments, jagged peaks, gorges and winding tree-lined watercourses.The range is best described as an escarpment with a height of 350 metres (1,150 ft) forming a tableland behind that slope gently to the South until it runs into the Hamersley Range. The steep escarpment is defined by a jumble of weathered basalts and granophyresThe highest point of the Chichester Range is Mount Herbert with a height of 367 metres (1,204 ft), the peak takes about 45 minutes to climb and a car park is at the base of the peak. The peak is also on the route of the Chichester Range Camel trail, a tourist attraction that is operated on the range that finishes at Python's Pool. The range is part of the Millstream-Chichester National Park, along with Millstream station that is one of the few permanent watercourses in the area.

Geologically the range is made up of a mixture sandstone, igneous rocks, and mineralised banded iron formation, being part of the Pilbara Craton.

The area was named by the explorer Francis Thomas Gregory in 1861 after the Parliamentary Under-Secretary of State for the Colonies Chichester Fortescue.The traditional owners of the area are the Bailgu or Palyku peoples, who speak the Yinjibarndi language

The range is the basis of two major river basins; the Fortescue Basin and the Port Hedland coast Basin.

The Port Hedland Coast Basin is the catchment area for many rivers including the Harding River, Sherlock River, Yule River and Shaw River.

Gondolin Cave is a fossiliferous dolomitic paleocave system in the Northwest Province, South Africa. The paleocave formed in the Eccles Formation dolomites (Malmani Subgroup, Chuniespoort Group carbonate-banded iron formation marine platform). Gondolin is currently the only described hominin-bearing fossil site in the Northwest Province-portion of the designated Cradle of Humankind UNESCO World Heritage Site. The cave is located on privately owned land and is not accessible to the public. As is the case with other South African Paleo-cave systems with Pliocene and/or Pleistocene fossil deposits, the system was mined for lime during the early 20th century. As a result, the system has been heavily disturbed and consists of only a small active cave, a series of in situ remnant cave deposits, and extensive dumpsites of ex situ calcified sediments produced during mining activities.

The Gunflint Range is an iron ore deposit in northern Minnesota in the United States and Northwestern Ontario, Canada. The range extends from the extreme northern portion of Cook County, Minnesota into the Thunder Bay District, Ontario.

The Gunflint Iron Formation is a continuation of the Mesabi Range to the southwest. The two have been separated by the intrusion of the Duluth Gabbro complex. The iron deposit is a banded iron formation of the Early Proterozoic Animikie Group. The Gunflint Iron Formation is overlain by "brecciated and complexly deformed iron formations", which in turn is overlain by ejecta from the "Sudbury meteorite impact event." This Sudbury Impact Layer is overlain by the Rove Formation. Stromatolite structures are evident within the Gunflint Iron Formation.The cherts of the Gunflint (the Gunflint Chert) are noted for containing Precambrian microfossils.

The Gunflint chert (1.88 Ga) is a sequence of banded iron formation rocks that are exposed in the Gunflint Range of northern Minnesota and northwestern Ontario along the north shore of Lake Superior. The black layers in the sequence contain microfossils that are 1.9 to 2.3 billion years in age. Stromatolite colonies of cyanobacteria that have converted to jasper are found in Ontario. The banded ironstone formation consists of alternating strata of iron oxide-rich layers interbedded with silica-rich zones. The iron oxides are typically hematite or magnetite with ilmenite, while the silicates are predominantly cryptocrystalline quartz as chert or jasper, along with some minor silicate minerals.

Stanley A. Tyler examined the area in 1953 and noted the red-colored stromatolites. He also sampled a jet-black chert layer which, when observed petrographically, revealed some lifelike small spheres, rods and filaments less than 10 micrometres in size. Elso Barghoorn, a paleobotanist at Harvard, subsequently looked at these same samples and concluded that "they were indeed structurally preserved unicellular organisms." In 1965 the two scientists published their finding, and named a variety of the Gunflint flora. This created an academic "stampede" to explore Precambrian microfossils from similar Proterozoic environments.

The Hamersley Range is a mountainous region of the Pilbara region of Western Australia. The range was named on 12 June 1861 by explorer Francis Thomas Gregory after Edward Hamersley, a prominent promoter of his exploration expedition to the worthwest.The range runs from the Fortescue River in the northeast, 460 km to the south. The range contains Western Australia's highest point, Mount Meharry, which reaches approximately 1,249 metres (4,098 ft) AHD. There are many extensively eroded gorges, such as Wittenoom Gorge. The twenty highest peaks in Western Australia are in the Hamersley Range. Peaks in the range include Mount Bruce (1,234 metres (4,049 ft)), Mount Nameless/Jarndunmunha (1,115 metres (3,658 ft)), Mount Reeder Nichols (1,109 metres (3,638 ft)), Mount Samson (1,107 metres (3,632 ft)), Mount Truchanas (1,148 metres (3,766 ft)) and Mount Tom Price (775 metres (2,543 ft)).Karijini National Park (formerly Hamersley National Park), one of Australia's largest national parks, is centred in the range.

The range contains large deposits of iron ore, producing a large proportion of Australia's iron ore exports. It is predominately associated with Banded Iron Formation (BIF).Western Australia's major iron producers have mines, communities and railways that occur along the range. Rio Tinto operates several iron ore mines within the range, including Mount Tom Price, Marandoo, Brockman, Channar, West Angelas, Mesa A mine, and Paraburdoo. Over 100 million tonnes of iron ore is removed from the range every year.In 1999 a small range within the Hamersley was named the Hancock Range after the Hancock family who were pioneers in the area. The Hancock range is east of Karijini National Park in a region of broad valleys and peaks that rise to almost 1,200 metres (3,937 ft). The Hancock Range is close to Mulga Downs Station, a property owned by the Hancock family and where Lang Hancock is buried.The traditional owners of the area that the range runs through are the Yindjibarndi peoples.

The Iron Quadrangle (Portuguese: Quadrilátero Ferrífero) is a mineral-rich region covering about 7,000 square kilometres (2,700 sq mi) in the central-southern part of the Brazilian state Minas Gerais. The area is known for its extensive deposits of gold, diamonds, and iron ore, being the source of approximately 40% of all gold produced in Brazil between the years 1500 and 2000. The deposits themselves pertain to the Minas Supergroup, a sequence of meta-sedimentary rocks initially formed in the Paleoproterozoic, about 2.5 Ga. In the 2010s, there have been two collapses of large tailings dams, which caused extensive damage and loss of life.

Iron mining in the United States produced 42.5 million metric tons of iron ore in 2015, worth US$3.8 billion. Iron ore was the third-highest-value metal mined in the United States, after gold and copper. Iron ore was mined from nine active mines and three reclamation operations in Michigan, Minnesota, and Utah. Most of the iron ore was mined in northern Minnesota’s Mesabi Range. Net exports (exports minus imports) were 3.9 million tons. US iron ore made up 2.5 percent of the total mined worldwide in 2015. Employment as of 2014 was 5,750 in iron mines and iron ore treatment plants.

US iron ore mining is dominated by the Precambrian banded iron formation deposits around Lake Superior, in Minnesota and Michigan; such deposits were also formerly mined in Wisconsin. For the past 50 years, more than 90 percent of US iron ore production has been mined from the Lake Superior deposits. None of the iron ore now mined in the US is “direct shipping” ore ready to be fed into the iron- and steel-making process. The ore is concentrated to raise the iron content before use. All the iron ore currently mined is from open pits.

Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in colour from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the form of magnetite (Fe3O4, 72.4% Fe), hematite (Fe2O3, 69.9% Fe), goethite (FeO(OH), 62.9% Fe), limonite (FeO(OH)·n(H2O), 55% Fe) or siderite (FeCO3, 48.2% Fe).

Ores containing very high quantities of hematite or magnetite (greater than about 60% iron) are known as "natural ore" or "direct shipping ore", meaning they can be fed directly into iron-making blast furnaces. Iron ore is the raw material used to make pig iron, which is one of the main raw materials to make steel—98% of the mined iron ore is used to make steel. Indeed, it has been argued that iron ore is "more integral to the global economy than any other commodity, except perhaps oil".

Jasper, an aggregate of microgranular quartz and/or chalcedony and other mineral phases, is an opaque, impure variety of silica, usually red, yellow, brown or green in color; and rarely blue. The common red color is due to iron(III) inclusions. The mineral aggregate breaks with a smooth surface and is used for ornamentation or as a gemstone. It can be highly polished and is used for items such as vases, seals, and snuff boxes. The specific gravity of jasper is typically 2.5 to 2.9. A green variety with red spots, known as heliotrope (bloodstone), is one of the traditional birthstones for March. Jaspilite is a banded iron formation rock that often has distinctive bands of jasper.

Jaspillite, or jaspilite, is a chemical rock formed similar to chert, but is generally quite iron rich. It is also known as jasper taconite. Jaspillite is typically a banded mixture of hematite and quartz common in the banded iron formation rocks of Proterozoic and Archaean age in the Canadian shield.

Jaspillite is also formed as exhalative chemical sediments in certain lead-zinc ore deposits, and as a hydrothermal alteration facies around submarine volcanism.

See also: Banded Iron FormationMPEG-4 Part 11 Scene description and application engine was published as ISO/IEC 14496-11 in 2005. MPEG-4 Part 11 is also known as BIFS, XMT, MPEG-J. It defines:

the coded representation of the spatio-temporal positioning of audio-visual objects as well as their behaviour in response to interaction (scene description);

the coded representation of synthetic two-dimensional (2D) or three-dimensional (3D) objects that can be manifested audibly or visually;

the Extensible MPEG-4 Textual (XMT) format - a textual representation of the multimedia content described in MPEG-4 using the Extensible Markup Language (XML);

and a system level description of an application engine (format, delivery, lifecycle, and behaviour of downloadable Java byte code applications). (The MPEG-J Graphics Framework eXtensions (GFX) is defined in MPEG-4 Part 21 - ISO/IEC 14496-21.)Binary Format for Scenes (BIFS) is a binary format for two- or three-dimensional audiovisual content. It is based on VRML and part 11 of the MPEG-4 standard.

MPEG-4 Binary Format for Scene (BIFS) is used in Digital Multimedia Broadcasting (DMB).The XMT framework accommodates substantial portions of SMIL, W3C Scalable Vector Graphics (SVG) and X3D (the new name of VRML). Such a representation can be directly played back by a SMIL or VRML player, but can also be binarised to become a native MPEG-4 representation that can be played by an MPEG-4 player. Another bridge has been created with BiM (Binary MPEG format for XML).

The Northeast Arm Iron Range, also called the Temagami Iron Range, is an elongated area of iron ore in Nipissing District of Northeastern Ontario, Canada. It parallels the western side of Lake Temagami's Northeast Arm near the village of Temagami at its northern end. One of many small iron ranges in the Temagami area, the Northeast Arm Range consists of alternating bands of iron-rich and iron-poor sediments. It was discovered in the 1890s and has since seen sporadic mining and mineral exploration activities.

The Nuvvuagittuq Greenstone Belt (NGB) is a sequence of metamorphosed mafic to ultramafic volcanic and associated sedimentary rocks (a greenstone belt) located on the eastern shore of Hudson Bay, 40 km southeast of Inukjuak, Quebec. These rocks have undergone extensive metamorphism, and represent some of the oldest rocks on Earth.

Two papers dating the age of the Nuvvuagittuq Greenstone Belt have been published. One paper gave an age of ca. 3,750 million years ago (mya), while the other gave an age of ca. 4,388 mya. In March 2017, the age of the Nuvvuagittuq Greenstone Belt was still unresolved.In March 2017, a published report gave evidence for fossils of microorganisms in these rocks, which would be the oldest trace of life yet discovered on Earth.

An ore is a natural occurrence of rock or sediment that contains sufficient minerals with economically important elements, typically metals, that can be economically extracted from the deposit. The ores are extracted at a profit from the earth through mining; they are then refined (often via smelting) to extract the valuable element, or elements.

The ore grade, or concentration of an ore mineral or metal, as well as its form of occurrence, will directly affect the costs associated with mining the ore. The cost of extraction must thus be weighed against the metal value contained in the rock to determine what ore can be processed and what ore is of too low a grade to be worth mining. Metal ores are generally oxides, sulfides, silicates, or native metals (such as native copper) that are not commonly concentrated in the Earth's crust, or noble metals (not usually forming compounds) such as gold. The ores must be processed to extract the elements of interest from the waste rock and from the ore minerals. Ore bodies are formed by a variety of geological processes. The process of ore formation is called ore genesis.

The Seminoe Mountains greenstone belt represents a fragment of an Archean greenstone terrane within the Wyoming craton. The greenstone belt was mapped by Hausel, who identified significant gold anomalies at Bradley Peak in banded iron formation, quartz veins and in a large altered zone of metabasalts. Mapping differentiated three mappable units that included the Bradley Peak metavolcanics, the Seminoe Formation and the Sunday Morning metasediments.

Mineral resources in the belt are varied, as is typical of most greenstone terranes. The mineral resources have not been explored in any great detail and indications are some deposits could be economic under favorable conditions. Low-grade iron deposits are widespread and include a minimum resource of 100,000,000 tons. Lapidary and decorative stone is varied and includes several types of attractive rock including serpentinite, leopard rock, jade, jasperized banded iron formation, and copper-coated (malachite, chrysocolla, cuprite) milky quartz. Copper mineralization is localized and does not represent a significant resource, as may be the same for zinc and lead.In past years, exploration efforts have been geared to the testing of narrow quartz veins and the possibility of broader auriferous pods enclosed in altered rock has been neglected. The altered zone in the vicinity of the Penn mines should have been considered as a target for widespread low-grade gold mineralization with potential credits in silver, copper, lead, and zinc.

Valentines iron formation is a banded iron formation found in Uruguay. It is composed of itabirite (or valentines) and gneiss.Containing a combination of minerals such as quartz, magnetite and pyroxene, it was named after the small town of Valentines by Prof. J. Bossi.

The Vermilion Range exists between Tower and Ely, Minnesota, and contains significant deposits of iron ore. Together with the Mesabi and Cuyuna Ranges, these three constitute the Iron Ranges of northern Minnesota; they were deposited in the Animikie Group. While the Mesabi Range had iron ore close enough to the surface to enable pit mining, mines had to be dug deep underground to reach the ore of the Vermilion and Cuyuna ranges. The Soudan mine was nearly 1/2 mile underground and required blasting of Precambrian sedimentary bedrock.The banded iron formation in the range consists of a "interbedded sequence" of chert, magnetite and hematite. Eleven mines operated in the range, with five in the Ely area. The Ely Trough, a synclinal fold, produced 70 million metric tons from the Chandler, Pioneer, Zenith, Sibley and Savoy mines. The largest mine in the range, Soudan, was closed in 1962, and the last mine in the Ely area closed in 1964.Despite the effort needed for the deep mining Soudan mine, the ore obtained was worth the effort; the quality of the hematite ore was so pure that two pieces could be welded. The bedrock, known as taconite, also contained iron, but in a much lower concentration. After more efficient practices for creating steel were discovered, the use of this high-quality ore was abandoned due to its more costly mining expense.

The Soudan hematite was used in the open hearth furnace, where the density of the ore, called Vermilion Lump, was needed to break through the floating slag to cause the molten charge to roil and burn off the impurities. When the newer blast furnaces came into use, the expensive Vermilion Lump was no longer needed. New processes were developed to extract the iron from the taconite by using open-pit mining. This method produced ore at a significantly reduced cost. Once proven successful, the technical change resulted in Minnesota's iron industry centering on the Mesabi Range, where the taconite was much easier to access.

This page is based on a Wikipedia article written by authors
(here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.